package com.smsc.headend.connector.utils;

public class GxFcsUtil {
    protected GxFcsUtil() {

    }

    private static int[] fcs16Table = { 0x0000, 0x1189, 0x2312, 0x329B, 0x4624,
            0x57AD, 0x6536, 0x74BF, 0x8C48, 0x9DC1, 0xAF5A, 0xBED3, 0xCA6C,
            0xDBE5, 0xE97E, 0xF8F7, 0x1081, 0x0108, 0x3393, 0x221A, 0x56A5,
            0x472C, 0x75B7, 0x643E, 0x9CC9, 0x8D40, 0xBFDB, 0xAE52, 0xDAED,
            0xCB64, 0xF9FF, 0xE876, 0x2102, 0x308B, 0x0210, 0x1399, 0x6726,
            0x76AF, 0x4434, 0x55BD, 0xAD4A, 0xBCC3, 0x8E58, 0x9FD1, 0xEB6E,
            0xFAE7, 0xC87C, 0xD9F5, 0x3183, 0x200A, 0x1291, 0x0318, 0x77A7,
            0x662E, 0x54B5, 0x453C, 0xBDCB, 0xAC42, 0x9ED9, 0x8F50, 0xFBEF,
            0xEA66, 0xD8FD, 0xC974, 0x4204, 0x538D, 0x6116, 0x709F, 0x0420,
            0x15A9, 0x2732, 0x36BB, 0xCE4C, 0xDFC5, 0xED5E, 0xFCD7, 0x8868,
            0x99E1, 0xAB7A, 0xBAF3, 0x5285, 0x430C, 0x7197, 0x601E, 0x14A1,
            0x0528, 0x37B3, 0x263A, 0xDECD, 0xCF44, 0xFDDF, 0xEC56, 0x98E9,
            0x8960, 0xBBFB, 0xAA72, 0x6306, 0x728F, 0x4014, 0x519D, 0x2522,
            0x34AB, 0x0630, 0x17B9, 0xEF4E, 0xFEC7, 0xCC5C, 0xDDD5, 0xA96A,
            0xB8E3, 0x8A78, 0x9BF1, 0x7387, 0x620E, 0x5095, 0x411C, 0x35A3,
            0x242A, 0x16B1, 0x0738, 0xFFCF, 0xEE46, 0xDCDD, 0xCD54, 0xB9EB,
            0xA862, 0x9AF9, 0x8B70, 0x8408, 0x9581, 0xA71A, 0xB693, 0xC22C,
            0xD3A5, 0xE13E, 0xF0B7, 0x0840, 0x19C9, 0x2B52, 0x3ADB, 0x4E64,
            0x5FED, 0x6D76, 0x7CFF, 0x9489, 0x8500, 0xB79B, 0xA612, 0xD2AD,
            0xC324, 0xF1BF, 0xE036, 0x18C1, 0x0948, 0x3BD3, 0x2A5A, 0x5EE5,
            0x4F6C, 0x7DF7, 0x6C7E, 0xA50A, 0xB483, 0x8618, 0x9791, 0xE32E,
            0xF2A7, 0xC03C, 0xD1B5, 0x2942, 0x38CB, 0x0A50, 0x1BD9, 0x6F66,
            0x7EEF, 0x4C74, 0x5DFD, 0xB58B, 0xA402, 0x9699, 0x8710, 0xF3AF,
            0xE226, 0xD0BD, 0xC134, 0x39C3, 0x284A, 0x1AD1, 0x0B58, 0x7FE7,
            0x6E6E, 0x5CF5, 0x4D7C, 0xC60C, 0xD785, 0xE51E, 0xF497, 0x8028,
            0x91A1, 0xA33A, 0xB2B3, 0x4A44, 0x5BCD, 0x6956, 0x78DF, 0x0C60,
            0x1DE9, 0x2F72, 0x3EFB, 0xD68D, 0xC704, 0xF59F, 0xE416, 0x90A9,
            0x8120, 0xB3BB, 0xA232, 0x5AC5, 0x4B4C, 0x79D7, 0x685E, 0x1CE1,
            0x0D68, 0x3FF3, 0x2E7A, 0xE70E, 0xF687, 0xC41C, 0xD595, 0xA12A,
            0xB0A3, 0x8238, 0x93B1, 0x6B46, 0x7ACF, 0x4854, 0x59DD, 0x2D62,
            0x3CEB, 0x0E70, 0x1FF9, 0xF78F, 0xE606, 0xD49D, 0xC514, 0xB1AB,
            0xA022, 0x92B9, 0x8330, 0x7BC7, 0x6A4E, 0x58D5, 0x495C, 0x3DE3,
            0x2C6A, 0x1EF1, 0x0F78

    };

    /*
     * Reserved for internal use.
     */
    public static final int countFCS16(final byte[] buff, final int offset,
                                       final int count) {
        int fcs16 = 0xFFFF;
        for (int pos = offset; pos < offset + count; ++pos) {
            fcs16 = (((fcs16 >> 8)
                    ^ fcs16Table[(fcs16 ^ (int) buff[pos]) & 0xFF]) & 0xFFFF);
        }
        fcs16 = ~fcs16;
        fcs16 = ((fcs16 >> 8) & 0xFF) | (fcs16 << 8);
        return (fcs16 & 0xFFFF);
    }

    /**
     * Reserved for internal use.
     *
     * @param buff
     * @param index
     * @param count
     * @return
     */
    private static final long CRCPOLY = 3551967744L;

    public static int countFCS24(final byte[] buff, final int index,
                                 final int count) {
        byte i, j;
        long crcreg = 0;
        for (j = 0; j < count; ++j) {
            int b = (buff[index + j] & 0xFF);
            for (i = 0; i < 8; ++i) {
                crcreg >>>= 1;
                if ((b & 0x80) != 0) {
                    crcreg |= 2147483648L;
                }
                if ((crcreg & 0x80) != 0) {
                    crcreg = crcreg ^ CRCPOLY;
                }
                b <<= 1;
            }
        }
        return (int) (crcreg >>> 8);
    }
}
